Age-related subcortical gray matter atropy, ventricular dilatation, and expansion of peripheral cerebrospinal fluid (CSF) volume were found in healthy men using magnetic resonance imaging (MRI), employing a threshold technique which allows quantification of volume. MRI showed a significant age related decrease of posterior frontal, but not of temporal lobe volume in healthy men. Men with mild Dementia of the Alzheimers type (DAT) had significantly less brain matter than did healthy age-matched controls. Discriminant analysis of MRI volumes completely separated DAT patients from healthy age- and sex-matched controls. Volumetric analysis of MRI images in Turner's syndrome (TS) revealed smaller hippocampi, basal ganglia and parieto-occipital brain matter than matched controls. Hippocampal volumes and memory test scores were reduced independently of 'X chromosome dosage' in TS subjects, suggesting a role for sex steroids in brain development and death of hippocampal neurons. White matter hyperintensities in healthy controls were found to predict increased ventricular volume, reduced brain volume, and reduced cognitive scores. Using 31P MR spectroscopy phosphorus metabolite concentrations were not found to differ between DAT patients and controls despite reduced glucose metabolic rates in the DAT patients. Disturbances in cellular phosphate energy reserves and membrane phosphoester metabolite levels do not appear to play a role in DAT.